Fibrous insulation is typically formed by fiberizing molten material and depositing the fibers on a collecting conveyor. Most, but not all fibrous insulation products contain a binder material to bond the fibers together, forming a lattice or network. The binder gives the insulation product resiliency for recovery after packaging, and provides stiffness and handleability so that the product can be handled and applied as needed in the insulation cavities of buildings. The fibrous insulation is cut into lengths to form insulation products, and the insulation products are packaged for shipping.
One typical insulation product is an insulation batt, usually about 8 feet long, and generally suitable for use as wall insulation in residential dwellings, or as insulation in the attic and floor cavities in buildings. In many insulation applications a vapor barrier is needed on one side or face of the insulation to prevent moisture-laden air from the warm interior of the dwelling from entering the insulation. Otherwise, the water vapor in the warm interior air cools and condenses within the insulation, thereby creating a wet insulation product which can have difficulty performing at its designed efficiency. Vapor barriers are typically created with a layer of asphalt in conjunction with a kraft paper or foil facing. Vapor barrier insulation products are commonly used to insulate walls, floors or ceilings that separate a warm interior space from a cold exterior space.
There are some insulation product requirements that call for insulation that is not vapor impermeable, but rather allows water vapor to pass through. For example, retrofit insulation products designed for adding additional insulation material on top of existing attic insulation should not have a vapor barrier. Also, insulation for wall cavities where the wall will have a separate full wall vapor barrier, such as a 4.0 mil polyethylene film on the interior or warm side of the wall, will not require a vapor barrier on the insulation product.
Recent advances in manufacturing insulation products have resulted in insulation materials that rely on encapsulation layers or films for containing and handling purposes, and do not require any binder material to bond the insulation fibers to each other. The encapsulation is particularly advantageous for binderless products or low binder products, although encapsulation provides benefits for many types of bindered products as well. An example of an encapsulated binderless product is disclosed in U.S. Pat. No. 5,227,955 to Schelhorn et al. Further, as disclosed in U.S. Pat. No. 5,545,279 to Hall et al., the insulation material can be encapsulated in an in-line process. The primary use for such encapsulated insulation products is attic insulation, although this type of insulation product can also be used in wall cavities or in underfloor ceiling cavities.
When applying encapsulation material to a fibrous batt the encapsulation material is attached to the fibrous batt by an adhesive layer or strip, such as a strip of hot melt adhesive applied in liquid form during manufacture of the insulation product. For example, the above-mentioned U.S. Pat. No. 5,277,995 to Schelhorn et al. discloses an encapsulated batt with an encapsulation material adhered with an adhesive that can be applied in longitudinal stripes, or in patterns such as dots, or in an adhesive matrix. The Schelhorn et al. patent also discloses that an alternative method of attachment is for the adhesive layer to be an integral part of the encapsulation film, which, when softened, bonds to the fibers in the batt.
A critical product attribute for building insulation products is the ability to resist or slow down the propagation of flames during a fire. It is important that building materials in general not be vehicles for rapid spread of flames or fire from one part of a building structure to another. Therefore, most building materials must meet flame spread limitations. A commonly used measure of the flame spread characteristics of a product is the ASTM E84 Tunnel Test for surface burning characteristics. In this test method a fire is generated at one end of a fire tunnel and the time required for the flames to spread 25 feet along the tunnel is measured. In another version of the test, the absolute distance along which the flames spread is measured. Another currently used test for the ability of insulation products to retard the spread of flames is the ASTM Radiant Panel Test. This test measures the flame spread characteristics of products subjected to radiation from a hot radiant panel suspended above the test specimen.
Various techniques have been proposed to reduce the flame spread of insulation products. One proposed solution is to incorporate fire retardant materials into the facing or encapsulation materials. Another method is to use an inorganic facing material, such as a foil material. Another solution is to employ inorganic adhesives to bind the encapsulation material to the fibrous batt. While some of these solutions can be effective in reducing the flame spread to acceptable levels, these solutions are generally relatively expensive.
It would be advantageous if there could be developed an economically acceptable means for reducing the flame spread of insulation products. Such insulation products should exhibit sufficiently low flame spread characteristics as to satisfy industry safety criteria, and should not appreciably raise the manufactured cost of the insulation product.